1. Field of Invention
The present invention relates to a method of fabricating optical fiber couplers by a fusion-elongation method for fabricating couplers by heating, fusing and elongating the parts of the gathered optical fibers.
2. Description of Prior Art
The optical fiber coupler is a device for splitting and coupling light passing through a plurality of optical fibers. The coupler is fabricated by heating, fusing and elongating the parts of the gathered optical fibers. To fabricate optical fiber couplers having a desired splitting ratio, the splitting ratio must be monitored in the fusion-elongation process.
The fusion-elongation method for fabricating the optical fiber couplers will be described in brief. The coatings of the parts of short optical fibers are removed. The coating-removed or exposed parts are brought together, heated, fused by a burner, for example, and elongated. One end of the optical fiber is connected to a light source (a semiconductor laser), while the other end is connected to photodetectors (optoelectric transducing elements). Light from the light source is introduced into the optical fiber at the first end thereof. Light emanating from the second end is monitored by the photodetectors. When a specific splitting ratio is reached, the operation of heating and elongating the exposed part is stopped (Japanese Patent Laid-Open Publication No. Sho. 63-175812).
A transmission monitor method has been known as one of the methods for monitoring the splitting ratio. FIG. 28 is an explanatory diagram showing an outline of the transmission monitor method. In the figure, reference numeral 1b designates a light source; 2a and 2b, optical fibers wound around bobbins; 3, an optical fiber coupler under fabrication; 6a and 6b, photodetectors; 7, a computer for computing splitting ratios; and 8a and 8b, V-grooves for fiber connection.
The light source 1b is a laser diode for generating laser light having the wavelength normally used. The coating-removed parts of the combined optical fibers 2a and 2b supplied from the bobbins for coupler fabrication purposes form an optical fiber coupler 3 under fabrication; that is, being subjected to the fusion-elongation process. The optical fibers are respectively connected at the ends to the optical fibers connecting to the photodetectors 6a and 6b at the V-grooves 8a and 8b. Laser light emitted from the light source 1b is led to the optical fiber 2a, passes through the coupler 3 under fabrication, and enters the photodetectors 6a and 6b. The light incident on the photodetectors 6a and 6b depends on the splitting conditions of the coupler 3 under fabrication. Accordingly, if the detected values are input to the computer 7, the computer may compute a splitting ratio. When a desired splitting ratio is reached, if the elongating operation is stopped, an optical fiber coupler having the desired splitting ratio can be fabricated.
In the transmission monitor method, at least one of the optical fibers coupled with the light source and the photodetector must be reconnected at the end every time one optical fiber coupler is formed. More specifically, in the case of FIG. 28, every time one coupler is formed, the coupler 3 is removed and a new coupler 3 is connected to the optical fibers of the photodetectors 6a and 6b at the fiber connection V-grooves 8a and 8b. The connection work is time consuming work, and if the connection is improper, measurement errors will be increased.